Transmission of pictures



Oct. 20, 1931. R. D. KELL TRANSMISSION OF PICTURES Filed July 8. 1929 Voltage lnvento 2 Rag D.KeU-. 9 WM I-lis Attorney.

Patented Oct. 20, 1931 UNITED STATES PATENT OFFICE BAY D. KELL, OF SCHENECTADY, NEW YORK, ASSIGNOR 'IO GENERAL ELECTRIC COM- PANY, A. CORPORATION OF NEW YORK TRANSMISSION OF PICTURES Application filed July 8, 1929. Serial No. 376,592.

My invention relates to transmission of pictures or the like, and has for its principal object the provision of an improved apparatus and method of operation which may be readily used to transmit or receive pictures by means of electrical impulses such as a high frequency carrier wave modulated in accordance with the shades of the picture to be transmitted.

lVIany of the picture transmitting apparatus heretofore provided include means for scanning the elemental areas of the picture, means for maintaining synchronism between the movable parts of the transmitting and receiving apparatus, and means for producing electrical impulses dependent on the intensity of the light reflected from the successive elemental areas of the picture.

The apparatus utilized to convert electrical impulses into light impulses may assume various forms. One form which has been used to some extent is a Kerr cell device such as that disclosed in a British patent of August Karolus 235,857. In the use of this device it has been proposed to utilize a moderately low direct current voltage applied between the plates of the cell. The use of such a voltage has the disadvantage that amplitude of the communicated signals must be comparatively high in order to modulate the light of the cell effectively. I have found that the application of a comparatively high voltage between the plates of the Kerr cell has the important advantages that a signal voltage of much lower amplitude may be utilized to control the light and that the cost of the modulating tube and other parts of the apparatus is greatly reduced.

My invention will be better understood from the following description when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a diagrammatic drawing of a picture receiving apparatus wherein my invention has been embodied; and Fig. 2 illustrates the relation existing between the bias voltage of the cell and the percentage of light transmitted through the cell.

The apparatus illustrated by Fig. 1 includes a picture receiving screen 10 upon which light is projected from a source 11, such as a high intensity are lamp through a lens 12, a lens 13, a shield or barrier 30, a Kerr cell 14:, such as that disclosed by the aforementioned patent, a lens 15, a lens disc 16 and lenses 17, 18 and 19. The shield 30 is interposed between the lens 13 and the cell 1 L for the purpose of protecting the cell from the light source 11. This part of the apparatus is well understood by those skilled in the art and need not be described in further detail.

The signals through which the light projected on the screen 10 is controlled are received by a radio receiver 20 and applied to the plates of the cell 14 through a valve 21 and a bias battery 22, a resistor 23 being connected in shunt with the cell and bias battery. A source of current shown as a battery 24 is connected between the cathode and anode of the valve 21 through a reactor 25. A resistor 26 and grid bias battery 27 are connected between the cathode and grid of this valve and the connection between the radio receiver and the grid of the valve is made through a condenser 28.

As previously indicated, I have found it to be desirable to make the bias voltage of the cell higher than that heretofore utilized. The advantages of this feature will be better un derstood upon reference to Fig. 2 in which the bias voltage of the cell 22 is plotted as abscissa and the percentage of light projected through the call 14 on the screen 10 is plotted as ordinates. It will be observed that the volt light characteristic of the cell changes with increase in the voltage and that the cell has a succession of volt light characteristics each of which has a different rate of change. The signal voltage required to vary the light between its maximum and minimum value depends on which characteristic is utilized in the operation of the apparatus. If the bias voltage from the cell is adjusted to the point A on the curve, the signal voltage must vary between B and C in order to vary the light from its minimum to maximum intensity. If the bias voltage of the cell is increased to D however, the signal voltage amplitude required for varying the light from maximum to minimum intensity is decreased approximately one-half and need only be varied from E to F.

As will be readily understood by those skilled in the art, the use of the higher bias voltage on the cell 14 has the very important advantage that the cell may be made smaller.

and may be practically constructed to operate with no greater signal voltage than is utilized in the operation of an ordinary loud speaker. The higher bias voltage is readily obtained from a rectifier of small size for the reason that the direct current transmitted through the cell is exceedingly small. The particular bias voltage utilized will of course depend on the dimensions of the cell. I have found that where the distance through the electrolyte is approximately 1/2" and the plate spacing .020 a bias voltage of 2600 volts is satisfactory. Heretofore such cells have been operated with a bias voltage of approximately 1200 volts and have been operated on the first volt light characteristic or on the part of the cell characteristic between the points B and C. In so far as I am aware, the advantages of operating the cell on one of the higher voltage characteristics had not been realized by those skilled in the art and it has not been proposed heretofore to operate the cell on other than its first volt light characteristic.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The method of utilizing a Kerr cell to control light in accordance with signal impulses which includes biasing said cell to one of its higher volt-light characteristics, and applying said impulses to said cell.

2. A picture transmitting system including a Kerr cell, means for projecting light through said cell, means for biasing said cell to one of its higher volt light characteristics, and means for applying a signal voltage to said cell.

3. The combination of a Kerr cell, means for subjecting said cell to a high bias voltage causing it to operate on one of its higher voltlight characteristics, and means for subjecting said cell to a signal voltage.

In witness whereof, I have hereunto set my hand this 5th day of July, 1929.

RAY D. ICELL. 

